The pathophysiology of sickle cell disease at the cellular and tissue level is poorly understood despite detailed information about the physical chemistry of hemoglobin S solutions. During the last few years we have been studying the intracellular polymerization of hemoglobin S and have detected polymer at high oxygen saturation. The present program is a multifaceted approach to study the rheological effects of polymer formation in red cells using electron microscopy, cell filterability and cell viscosity measurements. We are using electron microscopy to study the amount and physical properties of the polymer of deoxy-hemoglobin S that forms in sickle erythrocytes at various oxygen saturation values. The electron microscopic studies are being correlated with results from nuclear magnetic resonance spectroscopy and other methods to examine the physical, physiological and clinical variables that affect intracellular polymerization of deoxyhemoglobin S. These studies will allow us to test various hypothesis about the pathophysiology of sickle cell disease, specifically the relationship of the amount and length of the polymer to changes in cell rheology. These direct studies of polymer have been correlated with filterability and viscosity measurements in an attempt to understand how the amount of polymer and the rate of its formation impedes the flow of blood in the microcirculation of sickle cell patients. To facilitate these studies we have worked with BEIB o develop a filtration apparatus which allows us to measure deformability properties at various oxygen saturation values. This apparatus has allowed us to measure precisely several of the variables that determine the flow properties of sickle erythrocytes and try to correlate disease severity with these rheological measurements.